1. Field of the Invention
This invention relates to aberration compensation and more particularly relates to apparatus, methods, and systems for compensating for aberration when accessing an optical medium.
2. Description of the Related Art
Optical media have become increasing pervasive in digital systems. Movies, pictures, and other familiar content, as well as software programs, drivers, and data can all be stored in a non-volatile manner on optical media. Because the use of optical media is so flexible and pervasive, the motivation to increase storage density has increased. One approach to increasing the storage density of optical media involves the use of multiple data layers.
Accessing an optical media with multiple layers is typically accomplished by using a single laser and selecting a unique intensity for each data layer. For example, one intensity is set for the data layer closest to the laser, another intensity is set for the data layer farthest from the laser, and likewise for each data layer therebetween. Although the laser has multiple intensities to accommodate each data layer, the laser is typically set at a fixed focal length resulting in increased data error rates over single layer optical media.
Additional challenges result from the variability in optical characteristics from disk to disk and layer to layer. For example, variation in material composition or thickness may result in changes in the refractive index of the media and the desired focal point of the laser. Thus, the variability in optical characteristics and variation in layer depth as well as other factors result in increased aberration errors for multi-layered media.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that compensates for aberration on a layer by layer basis. Beneficially, such an apparatus, system, and method would reduce errors when accessing optical media and increase system robustness and performance.